Sharing of structured data in decentralized environments is a challenging problem, especially in the absence of a global schema. Social network structures map network links to semantic relations between participants in order to assist in efficient resource discovery and information exchange. In this work, we propose a scheme that automates the process of creating schema synopses from semantic clusters of peers which own autonomous relational databases. The resulting mediated schemas can be used

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... as global interfaces for relevant queries. Active nodes are able to initiate the group schema creation process, which produces a mediated schema representative of nodes with similar semantics. Group schemas are then propagated in the overlay and used as a single interface for relevant queries. This increases both the quality and the quantity of the retrieved answers and allows for fast discovery of interest groups by joining peers. As our experimental evaluations show, this method increases both the quality and the quantity of the retrieved answers and allows for faster discovery of semantic groups by joining peers. V Definition 1. Considering a relational schema S, a distinct concept corresponds to each R.A where A is an attribute of relation R ∈ S. A schema mapping between peers is actually a a set of concept correspondences that hold under a set of conditions. The conditions are either attribute joins or attribute value constraints. The following is the definition of a mapping: Definition 2. Considering a source schema S and a target schema S ′ , a GAV/LAV/GLAV mapping between them M(S, S ′ ) is the set {Cr M (S, S ′ ),Cond M (S, S ′ )}, where the set of concept correspondences Cr M (S, S ′ Obviously, for each pair of concepts {R.A, R ′ .A ′ } that each belong to a different schema, R.A ∈ S and R ′ .A ′ ∈ S ′ , and that are corresponded through a mapping M(S, S ′ ), there is one such pair in Cr M (S, S ′ ). A set of mappings between S, S ′ is denoted as Semantics are 'flooding' from one peer to the other, through respective mappings: Definition 3. For each correspondence R.A = R ′ .A ′ ∈ Cr M (S, S ′ ) ∈ M(S, S ′ ), the concepts, R.A, R ′ .A ′ are considered equivalent. Extended discussion and details on acquaintance mappings, query rewriting, query similarity etc can be found in [25] .